The present invention relates to an alkaline battery and a battery pack including a plurality of alkaline batteries which are packaged therein.
As shown in FIG. 6, a typical structure of an alkaline battery includes: a hollow cylindrical positive electrode 102, a cylindrical separator 104 with a bottom and a gelled negative electrode 103 which are provided in a cylindrical battery case 101 with a bottom. In the positive electrode 102 and the separator 104, an alkaline electrolyte is injected. An opening portion of the battery case 101 is sealed by crimping with a negative electrode terminal plate 106 and a gasket 105.
Since the gelled negative electrode 103 has a fluidity, there arises a problem in which, when a vibration or an impact is applied to the battery, the gelled negative electrode 103 leaks out between the separator 104 and the gasket 105 to the positive electrode 102 side and causes an internal short-circuit. Specifically, when a reaction area is increased by using rounded zinc alloy powder, which is a negative electrode active material, in order to increase a discharge capacity of the alkaline battery, a viscosity of the gelled negative electrode 103 is reduced and thus the above-described internal short-circuit is easily caused.
To cope with the above-described problem, conventionally, such leakage of a gelled negative electrode is prevented by adjusting a composition of materials of a separator or reducing a fiber orientation of a separator to improve a strength of the separator (see Japanese Patent Laid-Open Publication No. 2006-019094 and Japanese Patent Laid-Open Publication No. 2000-090939), or by providing a convex-shape bent portion at an edge portion of the separator to improve strength of contact between a separator and a gasket when the separator is attached to the gasket by pressure (see Japanese Patent Laid-Open Publication No. 2004-139843).
To increase a discharge capacity of an alkaline battery, it is effective to reduce a thickness of a battery case and correspondingly increase an inner volume of the battery. However, if the thickness of the battery case is reduced, a crimp strength of a sealing portion of the battery case is reduced and might cause leakage of an electrolyte from the sealing portion. As a measure to cope with this problem, the opening portion of the battery case is formed to have a larger thickness than a thickness of a body portion (Japanese Patent Laid-Open Publication No. 2002-151017 and Japanese Patent Laid-Open Publication No. 5-089861).